This invention relates to improvements in apparatus and method for recovering oil spills on open water and more particularly to means for confining and directing oil spills into a pick-up or recovery device such as that disclosed in co-pending J. A. McGrew patent application Ser. No. 327,007, filed Jan. 26, 1973. While the invention is herein described in its presently preferred embodiment, it will be recognized that certain modifications and changes may be made without departing from the essential features involved.
With most oil spill recovery devices operable on open water, such as a skimmer vessel employing a low-resistance flow-through reticular matrix pick-up belt of the characteristics described in the above-cited application, it is important that the oil remain at or near the surface either in a layer or at least in globules of a size that can be readily separated from the water. If unduly agitated immediately preceding or in connection with the recovery operation, the oil may be dispersed in very small particles, or even emulsified, so that it cannot be effectively picked up by the matrix, or by currents, much of it circulated below the surface out of reach of the pick-up device.
A principal technique previously used to confine and direct an oil spill so that it could be picked up by a recovery device consisted in the deployment of elongated floating booms or curtains stretched out along the edge or around the perimeter of the spill. These devices employed floats and formed a long physical barrier often half a mile or greater in length, making them awkward to deploy and very difficult to move or control once positioned. Usually, a positioning tug or other vessel made fast to each end of the barrier boom was necessary to hold it in place or move it about. Moreover, in choppy, rough water, slop-over could allow oil from the spill to escape over the boom. Experience also reveals that even with a boom having a barrier curtain suspended beneath it, currents may carry oil under the boom substantially without regard to depth of the curtain. Such oil spill confinement booms, while useful in certain situations, were not at all suited for mobile use in physical association with skimmer vessels having to travel at substantial speeds through the water in order to work a large area.
As an alternative to the floating boom, Muhler U.S. Pat. No. 3,659,713 discloses a non-submersion type mobile boom system employing gaseous discharge curtains to sweep and move or confine the spill. According to that patent, sheets of air moving downward at high velocity on an incline into impingement with the surface of the water will sweep the oil ahead of it, whereby it can be funneled effectively into the path of a recovery vessel. The stated purpose of using air in that case was to produce the desired "herding" or sweeping action without dispersing or emulsifying the oil, it apparently having been recognized that the long-standing use of streams of water discharged through hoses to move a spill did cause temporary dispersal and/or some emulsification.
With forced air curtains, particularly with booms of any substantial length disposed above the water's surface along the desired perimeter or edge zones as in the above-mentioned patent, large volumes of air would have to be compressed and distributed under substantial pressure from a slotted boom maintained at a suitable elevation in order to provide the necessary sweeping force at the water's surface to effectively confine or move the oil. Particularly this will be true when attempting to operate on windy days and/or in open water with the booms elevated clear of wave crests as they must be. Under these conditions, moreover, the effectiveness of the sheet of air impinging the surface of the wave crests situated near the boom will be much greater than in the troughs, sometimes a matter of feet below the crests. The same U.S. Pat. No. 3,569,713 mentions the possibility of pumping water or other liquid through the same slotted booms; however, it is found that sheets of water forcibly directed against the edge of an oil spill churn up the water and oil and are therefore self-defeating in applications wherein dispersal, pumping and emulsification of the oil presents problems.
A chief object of the present invention is to devise an improved non-submersion type boom or similar oil spill confining, sweeping or directing apparatus and method overcoming the aforementioned difficulties and limitations. More specifically, it is an object hereof to provide a new and improved, economic and versatile system and technique for sweeping surface oil which utilizes cross-sectionally elongated fluid discharge curtains or patterns of force-producing flow directed against the water's surface, and which may employ discharge booms or the like maintained at suitable elevation above the water's surface, yet operate effectively under varying conditions of wind, swells, and chop. A related object is to devise such a system which may be used to advantage both in stationary recovery installations as well as in conjunction with and as part of highly mobile and rapid moving skimmer vessels.
A further and more specific object hereof is to devise such a system and technique wherein water itself may be utilized effectively to create the required fluid flow forces acting on the oil spill, and such that the cost, weight and space economics of a simple pump, conduit and nozzle arrangement present additional advantages in the improved apparatus.
A further object hereof is to devise an effective oil spill confining and directing system and method operable on or in direct physical association with a rapid-moving oil spill recovery (skimmer) vessel without appreciable escapement of the oil due to dispersal or emulsification or to leakage through or around the fluid flow curtain confining and directing part of the system.